1. Field of the Invention
The present invention relates to a mobile terminal.
2. Related Art
A handover technique where a mobile terminal switches and uses a plurality of different networks, such as cellular system access networks like a PHS, a GPRS, a CDMA, and an HSDPA and an access network like 802.11 and 802.16, in accordance with a necessity has been known (refer to JP-A 2005-244590 (KOKAI)). The handover technique is generally called a vertical handover technique.
The vertical handover is realized using protocols, such as Mobile IPv4, Mobile IPv6, MOBIKE (IKEv2 Mobility and Multihoming) protocol. Further, it is known that the technique called a soft handover reduces the number of packet losses when a terminal switches the network by these protocols.
Soft handover maintains the connection to the previous network for a while even after the terminal is connected to the new network. As a result, the terminal can securely receive all of the packets passing through the previous network while network switching.
Further, during the handover process, a relay apparatus (home agent) that provides mobility to the terminal also maintains a connection to the previous network after switching the network for a while. As a result, the relay apparatus can securely receive all of the packets passing through the network before switching, during a network switching process and transmit the packets.
A soft handover method according to the related art at the time of vertical handover using Mobile IPv4 will be described. Hereinafter, the soft handover at the time of a vertical handover is simply referred to as handover. In this case, the case where a mobile terminal switches from a cellular network to a wireless LAN will be described.
Before a handover, a tunnel via a cellular network is established between a mobile terminal and a home agent, and a cellular network interface of the mobile terminal receives packets transmitted from a counterpart apparatus.
The mobile terminal determines that it switches the network to a wireless LAN, when the signal strength from a wireless LAN base station becomes sufficiently strong. Then a Registration Request message is transmitted from the wireless LAN interface of the mobile terminal to the home agent.
The home agent receives the Registration Request message and detects that the mobile terminal requires to switch the network. Then the home agent transmits a Registration Reply message, which describes that the mobile terminal is allowed to switch network, to the wireless LAN interface of the mobile terminal.
The home agent changes configurations of the tunnel such that the packet transmitted from the counterpart apparatus is transferred to the wireless LAN interface of the mobile terminal, in accordance with reception of the Registration Request message or transmission of the Registration Reply message.
Further, if the mobile terminal receives the Registration Reply message, the mobile terminal configures a new tunnel so that the mobile terminal can receive the packet transferred from the home agent to the wireless LAN interface. Thereby, the mobile terminal can receive the packet transferred from the home agent by both of the wireless LAN interface and the cellular network interface.
In general, a communication delay of the cellular network is larger than a communication delay of the wireless LAN. For this reason, at a point of time when the packet is first received in the wireless LAN interface, the mobile terminal does not receive the packet that the home agent has transmitted to the cellular network interface of mobile terminal.
Even after establishing the new tunnel through the wireless LAN, the mobile terminal keeps configuration of the tunnel through the cellular network, and deletes the configuration of the tunnel after a sufficient time passes. Thereby, it is possible to receive all of the packets transmitted from the home agent to the cellular network interface without causing a packet loss at the time of the handover.
However, in the handover method according to the related art, since the mobile terminal cannot detect a point of time when the mobile terminal receives all of the packets transmitted from the home agent to the cellular network (network before the handover) interface, the configuration of the tunnel is not deleted for some time after all of the packets are received, and power that is supplied to the cellular network interface cannot be stopped.
In this case, it is not possible to release a memory resource to keep the configuration that allows the packets transmitted from the home agent to be received by the cellular network interface.